Lettuce is the crop controlled-environment growing was practically built around: cool, fast, low-light, and forgiving. Get a few numbers right and it almost grows itself.
What it wants
Lettuce asks for less than most crops. The whole profile is cool and light:
- Temperature, 60 to 70°F by day, a little cooler at night. Push past about 75°F and it bolts and tipburns.
- Light, a modest DLI of 12 to 17 mol/m²/day. Lettuce is a low-light crop, and too much light brings on tipburn faster than it adds growth.
- Feeding, pH 5.5 to 6.0 and a light EC of 0.8 to 1.2 mS/cm. It is a gentle feeder.
- Humidity and air, steady airflow over the canopy. Still, humid air is the classic tipburn setup.
- Roots, cool and well-oxygenated. NFT and deep-water culture both suit it.
The arc
From seed, lettuce germinates in two or three days, spends two to three weeks as a transplant, and heads up for harvest about four to six weeks after going into the system. The short cycle is what makes a staggered planting pay: seed a new tray every week and you cut a steady supply instead of a glut.
What it fears
Two things spoil lettuce, and both trace back to heat and air. Tipburn (brown, crispy leaf margins) is a local calcium shortfall, usually because the inner leaves transpire too little in still, humid air, not because the feed lacks calcium. Move air across the canopy and ease the light. Bolting (the plant shooting up to flower, turning bitter) is the heat signal: keep it cool and harvest before it starts. Warm roots also invite Pythium, so keep the solution cool.
Getting it right
Pick a few varieties and learn their timing before adding more. Keep the canopy cool and the air moving, feed lightly, and harvest before heat makes the decision for you. Loose-leaf and butterhead types are the easiest start; the cultivar browser helps match one to your climate. Log days-to-harvest and any tipburn against your conditions, and as data is king puts it, keep that record yours.
Tools for this crop
Frequently asked questions.
What pH and EC does hydroponic lettuce need?
Lettuce does best at pH 5.5 to 6.0 with a light nutrient strength of about EC 0.8 to 1.2 mS/cm. It is a gentle feeder, so a strong solution does more harm than good. Hold the pH steady and keep the solution cool and well-oxygenated.
Why does my lettuce get tipburn?
Tipburn (brown, dry leaf edges) is a local calcium shortage in the fast-growing inner leaves, usually caused by still, humid air rather than a lack of calcium in the feed. The inner leaves transpire too little to pull calcium to the margins. Move air across the canopy, ease back the light, and avoid heat spikes.
How much light does lettuce need?
A daily light integral of about 12 to 17 mol/m²/day is plenty. Lettuce is a low-light crop, and pushing more light tends to bring on tipburn and bolting faster than it adds usable growth.